It is highly desirable for tires to have good wet skid resistance, low rolling resistance, and good wear characteristics. It has traditionally-been very difficult to improve a tire's wear characteristics without sacrificing its wet skid resistance and traction characteristics. These properties depend, to a great extent, on the dynamic viscoclastic properties of the rubbers utilized in making the tire.
In order to reduce the rolling resistance and to improve the treadwear characteristics of tires, rubbers having a high rebound have traditionally been utilized in making tire tread rubber compounds. On the other hand, in order to increase the wet skid resistance of a tire, rubbers which undergo a large energy loss- have generally been utilized in the tire's tread. In order to balance these two viscoelastically inconsistent properties, mixtures of various types of synthetic and natural rubber are normally utilized in tire treads. For instance, various mixtures of styrene-butadiene rubber and polybutadiene rubber are commonly used as a rubbery material for automobile tire treads.
ESBR/silica systems give rise to tread compounds with excellent tear/tensile properties, good wet performance, but tend to be deficient in rolling resistance and wear properties. Mid-styrene SSBR silica systems give rise to tread compounds with excellent wet/rolling resistance/wear balance, but they tend to be somewhat deficient in tear/tensile properties.